X-ray tubes typically utilize an x-ray transmissive window formed in the vacuum enclosure of the x-ray tube that permits x-rays produced within the x-ray tube to be emitted from the housing and into an intended target. The window is typically set within a mounting structure, and is located in a side or in an end of the x-ray tube. The window separates the vacuum of the vacuum enclosure of the x-ray tube from the normal atmospheric pressure found outside the x-ray tube or from the pressure of a liquid coolant in which the x-ray tube is submerged.
Although window thicknesses vary depending on the particular x-ray tube application, windows are typically very thin. In particular, a window with a reduced thickness is generally desired so as to minimize the amount of x-rays that are absorbed by the window material during x-ray tube operation.
While a thinner window is desirable, a thin window is typically subjected to deforming stresses during the operation of the x-ray tube. One of the major challenges in developing x-ray tubes for modern, high performance x-ray systems is to provide design features to accommodate the high levels of heat produced. To produce x-rays, relatively large amounts of electrical energy must be transferred to an x-ray tube. Only a small fraction of the electrical energy transferred to the x-ray tube is converted into x-rays, as the majority of the electrical energy is converted to heat. If excessive heat is produced in the x-ray tube, the temperature can rise above critical values, and the window of the x-ray tube can be subject to thermally-induced deforming stresses. Such thermally-induced deforming stresses are non-uniformly distributed over the surface of the window and can produce cracking in the window, as well as leaks between the window and the mounting structure.
One portion of the window which is frequently deformed during x-ray tube operation due to relatively high heat is the portion of the window that is bonded to the mounting structure. The deformation of the window can result in cracking of the window and consequent loss of vacuum from the x-ray tube housing, and thereby limit the operational life of the x-ray tube.
In addition to increasing the likelihood of a cracked window, the heat produced during x-ray tube operation can also result in the boiling of liquid coolant in which the x-ray tube is submerged and that is in direct contact with the window. This boiling of the liquid coolant can result in detrimental attenuations in the x-rays as they pass through the boiling liquid on their way to the intended target. This detrimental attenuation of the x-rays can cause defects in the resulting x-ray images of the target, which can result, for example, in a misdiagnosis of a patent being x-rayed.